Java通过MyBatis框架对MySQL数据进行增删查改的基本方法

时间:2021-10-31 03:43:19

1. 查询

除了单条记录的查询,这里我们来尝试查询一组记录。

IUserMapper接口添加下面方法:

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List<User> getUsers(String name);

在User.xml中添加:

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<resultMap type="User" id="userList"><!-- type为返回列表元素的类全名或别名 -->
  <id column="id" property="id" />
  <result column="name" property="name" />
  <result column="age" property="age" />
  <result column="address" property="address" />
</resultMap>
 
<select id="getUsers" parameterType="string" resultMap="userList"><!-- resultMap为上面定义的User列表 -->
  select * from `user` where name like #{name}
</select>

测试方法:

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@Test
public void queryListTest() {
  SqlSession session = sqlSessionFactory.openSession();
  try {
    IUserMapper mapper = session.getMapper(IUserMapper.class);
    List<User> users = mapper.getUsers("%a%"); // %在sql里代表任意个字符。
    for (User user : users) {
      log.info("{}: {}", user.getName(), user.getAddress());
    }
  } finally {
    session.close();
  }
}

如果联表查询,返回的是复合对象,需要用association关键字来处理。
如User发表Article,每个用户可以发表多个Article,他们之间是一对多的关系。

(1) 创建Article表,并插入测试数据:

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-- Drop the table if exists
DROP TABLE IF EXISTS `Article`;
 
-- Create a table named 'Article'
CREATE TABLE `Article` (
  `id` int NOT NULL AUTO_INCREMENT,
  `user_id` int NOT NULL,
  `title` varchar(100) NOT NULL,
  `content` text NOT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=1 DEFAULT CHARSET=utf8;
 
-- Add several test records
INSERT INTO `article`
VALUES
('1', '1', 'title1', 'content1'),
('2', '1', 'title2', 'content2'),
('3', '1', 'title3', 'content3'),
('4', '1', 'title4', 'content4');

(2) com.john.hbatis.model.Article类:

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public class Article {
  private int id;
  private User user;
  private String title;
  private String content;
  // Getters and setters are omitted
}

(3) 在IUserMapper中添加:

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List<Article> getArticlesByUserId(int id);

(4) 在User.xml中添加:

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<resultMap type="com.john.hbatis.model.Article" id="articleList">
  <id column="a_id" property="id" />
  <result column="title" property="title" />
  <result column="content" property="content" />
   
  <association property="user" javaType="User"><!-- user属性映射到User类 -->
    <id column="id" property="id" />
    <result column="name" property="name" />
    <result column="address" property="address" />
  </association>
</resultMap>
 
<select id="getArticlesByUserId" parameterType="int" resultMap="articleList">
  select u.id, u.name, u.age, u.address, a.id a_id, a.title, a.content
  from article a
  inner join user u
  on a.user_id=u.id and u.id=#{id}
</select>

(5)测试方法:

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@Test
public void getArticlesByUserIdTest() {
  SqlSession session = sqlSessionFactory.openSession();
  try {
    IUserMapper mapper = session.getMapper(IUserMapper.class);
    List<Article> articles = mapper.getArticlesByUserId(1);
    for (Article article : articles) {
      log.info("{} - {}, author: {}", article.getTitle(), article.getContent(), article.getUser().getName());
    }
  } finally {
    session.close();
  }
}

附:
除了在association标签内定义字段和属性的映射外,还可以重用User的resultMap:

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<association property="user" javaType="User" resultMap="userList" />

2. 新增

IUserMapper接口添加下面方法:

int addUser(User user); 

User.xml添加:

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<insert id="addUser" parameterType="User" useGeneratedKeys="true" keyProperty="id"><!-- useGeneratedKeys指定myBatis使用数据库自动生成的主键,并填充到keyProperty指定的属性上。如果未指定,返回对象拿不到生成的值 -->
  insert into user(name,age,address) values(#{name},#{age},#{address})
</insert>

测试方法:

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@Test
public void addUserTest() {
  User user = new User("Lucy", 102, "Happy District");
  SqlSession session = sqlSessionFactory.openSession();
  try {
    IUserMapper mapper = session.getMapper(IUserMapper.class);
    int affectedCount = mapper.addUser(user);
    session.commit(); // 默认为不自动提交。调用session.getConnection().getAutoCommit()查看
    log.info("{} new record was inserted successfully whose id: {}", affectedCount, user.getId());
  } finally {
    session.close();
  }
}

3. 更新

接口添加方法:

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int updateUser(User user);

User.xml添加:

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<update id="updateUser" parameterType="User">
  update `user` set name=#{name}, age=#{age}, address=#{address}
  where id=#{id}
</update>

测试方法:

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@Test
public void updateUserTest() {
  SqlSession session = sqlSessionFactory.openSession();
  try {
    IUserMapper mapper = session.getMapper(IUserMapper.class);
    User user = mapper.getUserById(8);
    user.setAddress("Satisfied District");
    int affectedCount = mapper.updateUser(user); // 除了要修改的属性外,user的其它属性也要赋值,否则这些属性会被数据库更新为初始值(null或0等),可以先查询一次,但这样会增加和数据库不必要的交互。后面的条件判断能避免此问题。
    log.info("Affected count: {}", affectedCount);
    session.commit();
  } finally {
    session.close();
  }
}

 4. 删除

接口添加方法:

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int deleteUser(int id);

User.xml添加:

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<delete id="deleteUser" parameterType="int">
  delete from `user` where id=#{id}
</delete>

测试方法:

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@Test
public void deleteUserTest() {
  SqlSession session = sqlSessionFactory.openSession();
  try {
    IUserMapper mapper = session.getMapper(IUserMapper.class);
    int affectedCount = mapper.deleteUser(8);
    log.info("Affected count: {}", affectedCount);
    session.commit();
  } finally {
    session.close();
  }
}